NMR logging using time-domain averaging

Abstract

Method for data acquisition and processing, which uses time-domain averaging to increase the signal to noise ratio (SNR) in single-event measurements. In a preferred embodiment, NMR echo-trains obtained using high-speed NMR logging are provided, the echo trains are time-domain averaged, preferably in real-time, over one or more time intervals to sharpen the spatial resolution of the logging tool and / or to increase the signal to noise ratio (SNR) of the data train.

Description

FIELD OF THE INVENTION[0001]The present invention concerns logging applications and more specifically relates to a method for data acquisition and processing, which uses time-domain averaging to increase the signal to noise ratio (SNR) or to sharpen the spatial resolution of the obtained logging data. In an exemplary application, the method is used in nuclear magnetic resonance (NMR) logging to increase the SNR of single event echo-train for high-speed NMR logging and / or to sharpen the spatial resolution of the received data.BACKGROUND OF THE INVENTION[0002]In oil and gas exploration it is desirable to understand the structure and properties of the geological formation surrounding a borehole, in order to determine if the formation contains hydrocarbon resources (oil and / or gas), to estimate the amount and producibility of hydrocarbon contained in the formation, and to evaluate the best options for completing the well in production. A significant aid in this evaluation is the use of ...

AI Technical Summary

Benefits of technology

[0012]In a preferred embodiment the present invention uses time-domain average of single event data to increase the SNR, but not stacking of data from multiple events, and hence, achieves higher spatial resolution. In accordance with the present invention, the SNR can be increased also by application of both the time-domain-average and stacking techniques. In such case, high spatial resolution can be achieved using a lesser number of stacking events. Various combinations of techniques known in the art with the teachings of the present invention are possible in this regard and will be appreciated by a person of skill in the art.

Problems solved by technology

When the logging speed is slow, the tool moves only a short distance.

However, when the logging speed is relatively fast, the tool moves over longer distances and the formation properties may change significantly over the distance.

As a result, stacking of echo train data from multiple events, as generally used in the prior art, reduces apparent spatial resolution of measuremenets beyond the intrinsic resolution of the tool.

Enhancing the resolution of the logs is a significant problem, because subsurface formations are generally heterogeneous, so that porosity, saturation and lithology vary with position.

In such cases, the petrophysical evaluation of one layer may be distorted by the presence of another layer falling within the larger volume of investigation of the tool.

The above phenomenon leads to a specific problem in the analysis of subsurface formations that include one or more underground layers, especially when the layers are thin compared with the vertical resolution of the measuring tool.

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